Keep in mind that the spec'd distortion levels on components means almost nothing. For starters, a manufacturer will never reveal the spectra of the distortion generated, especially if it consists completely of odd order harmonics. Additionally, in the case of power amplifiers, the distortion measurements are taken at higher wattages where the ratio of distortion to signal is greatest. If you look at the distortion verses output plots of most amplifiers, you will see that the distortion is much higher at low levels, such as around 1 watt, where most actual listening takes place.

A favorite manufacturer's argument is that since distortion is "so low" to start with, the fact that it is odd order doesn't matter. Nothing could be farther from the truth. Our ears can hear levels of 5th, 7th, 9th etc odd order distortion that "measure" in the .00x% range as a hardening and sterile quality to the sound.

In contrast, most people cannot hear 2nd order harmonic distortion at levels even exceeding 1% to 5% since the even order components are directly musically realated as the simple addition of octaves above the original frequencies.